Senator John Kerry ratcheted up the fight to pass legislation to combat global warming on Wednesday, unveiling a bill as the Gulf of Mexico oil disaster complicates the measure's already difficult prospects this year.

Kerry, a Democrat, and Senator Joseph Lieberman, an independent, took the wraps off their bill as two important deadlines loom.

Congressional elections are less than six months away and with Democrats facing losses, June or July could be the last chance for them to pass a climate bill this year, before the political atmosphere gets too overheated.

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Then there's the Environmental Protection Agency, which stands ready to put regulations into effect in January that would reduce carbon dioxide pollution from power plants and factories if Congress fails to act.

"If we got into the floor in June or July, I'd be very happy," Kerry told reporters.

Foreign capitals will be watching Congress and the EPA closely, as the fate of an international pact to battle global warming hangs largely on Washington's actions.

A Republican supporter of the U.S. climate legislation, which aims to cut planet-warming domestic emissions by a modest 17 percent in the next decade, was conspicuously absent on Wednesday.

Republican Senator Lindsey Graham, who worked with the two senators on the bill, did not attend the ceremony to unveil it. He reiterated in a statement that this is not the time to press on a climate bill because of the massive oil leak and talk of moving ahead on immigration reform.